1. Field of the Invention
This invention relates to a (thio)epoxy compound suitably used in the field of resins such as optical materials including plastic lenses, prisms, optical fibers, information recording media and light emitting diodes which are required to have a high refractive index and a high transparency, as well as resins therefrom.
This invention also relates to a polymerizable composition suitably used as a starting material for a plastic lens for eyeglasses.
2. Description of the Related Art
A plastic lens is lighter and less brittle than an inorganic lens, and dyeable, which has been therefore rapidly prevailing in the areas of optical devices such as a lens of eyeglasses and a camera lens. Such a plastic lens is required to exhibit optical properties including a high refractive index and a high Abbe number and physical properties including high heat resistance and a low specific gravity.
Among these, high heat resistance and a low specific gravity have been considerably achieved by a current plastic lens with a high refractive index. Currently, the resins which may be widely used for these applications, include those prepared by radical polymerization of diethylene glycol bis(allylcarbonate) (referred to as "D.A.C."). These resins have various features such as excellent impact resistance, lightness, excellent dye-affinity, and good processability including machinability and abradability. These resins, however, have a low refractive index (nd) of about 1.50, leading to a lens with thick center and margin. Thus, there is a need for a resin for a lens with a higher refractive index.
Resins with a higher refractive index than D.A.C. resin are known; for example, polythiourethane resins (e.g., JP-A 63-46213); sulfur-containing O-(meth)acrylate resins (e.g., JP-A 1-128966, 3-217412 and 4-16141); and thio(meth)acrylate resins (e.g., JP-A 63-188660 and JP-B 3-59060), in which sulfur atoms are introduced. A polythiourethane resin is well-balanced in its properties, that is, having suitable properties such as a high refractive index and good impact resistance.
A refractive index and an Abbe number are, however, conflicting properties; as the refractive index increases, the Abbe number decreases. It is, therefore, quite difficult to simultaneously improve these properties. Thus, it has been intensively investigated to achieve a high refractive index, preventing an Abbe number from being decreased.
Most typical suggestions of these attempts are processes using a (thio)epoxy compound as described in JP-As 9-110979, 9-71580 and 9-255781.
According to the processes, a high refractive index can be achieved while maintaining a relatively high Abbe number. A resin prepared according to these processes exhibits a refractive index of nd=about 1.70. Thus, it cannot be considered to meet the need for an improved refractive index sufficient to make a margin of an eyeglass significantly thinner while maintaining a high Abbe number, compared with a commercially available common lens with nd=1.67. An thioepoxy resin prepared from an thioepoxy compound tends to turn yellow during heating in a secondary process, long-term storage or its use. Such yellowing may cause tone alteration of an eyeglass which is required to be fashionable. Thus, it may not meet the needs of routine users of eyeglasses. A procedure for solving the problem has been suggested in, e.g., JP-A 10-298287, where a thiol compound is added to an thioepoxy compound to prevent yellowing. Although such a process can prevent yellowing, addition of a thiol compound, especially a mono- or bis-functional thiol, may cause significant deterioration of heat resistance, resulting in a lens which cannot give sufficient properties for an application requiring higher heat resistance.